Abstract Osteoarthritis (OA) is the most common chronic condition among older adults, is a major barrier to their participation in physical activity, and is a known risk factor for disability and institutionalization. Fit and Strong! is an evidence-based physical activity/behavior change program that targets this high risk group. It addresses documented strength and aerobic deficits in this population and is inexpensive and simple to replicate. Results from a randomized trial show that Fit and Strong! has significantly decreased participants'lower extremity joint pain and stiffness while increasing their self efficacy for exercise and their maintenance of exercise over time (Hughes et al, 2004 and Hughes et al., 2006). Fit and Strong! is currently being replicated in Chicago, in Charlotte, NC and in WVA. It is ready for broad, community-based diffusion to persons who can benefit from it. Because little is currently known about the most effective ways of translating and diffusing physical activity programs for older adults, this study will examine the effectiveness of partnering with existing Area Agencies on Aging (AAAs) in two states (IL and NC) to translate and diffuse the program to senior centers within two AAA catchment areas per state. This translation study will use Glasgow's Re-Aim model and Greene et al.'s work on evaluation (Glasgow, Vogt and Bowles, 1999;Green and Glasgow, 2006) to identify facilitators and barriers to the reach, effectiveness, adoption, implementation and maintenance of Fit and Strong!. We will train a T Trainer and Master Trainers and will work with them to train certified exercise instructors to conduct Fit and Strong at senior centers in 4 AAA catchment areas (target Ns = 1 T trainer, 2 master trainers, 30 sites, 30 certified instructors and a minimum of 1,200 participants). The study will use mixed methods including secondary analyses of census and BRFS data (reach), pre-postest participant outcome measures (effectiveness), surveys of all senior centers in each catchment area (adoption), site visits to all participating Centers to develop and refine fidelity/adaptation checklists and procedures (implementation), and in-depth interviews with upper level senior center managers at the conclusion of each iteration of Fit and Strong! (maintenance) to evaluate the effectiveness of this diffusion process along with facilitators and barriers experienced within and across the two states. Study funds will also be used to develop a Fit and Strong! website and an interactive web-based support hotline, to finalize training materials, to support the cost of the trainings and to provide financial incentives for participation among the first sites that sign up to participate. Study activities will both advance the development of Fit and Strong as a high quality, turnkey evidence based program and also obtain new data on factors that facilitate the adoption, implementation, and maintenance of PA programs for older adults.